1. Field of the Invention
The present invention relates to a recording method and apparatus for recording information on an optical disc by forming a recoding mark with a different physical property from other portions on the recording medium.
2. Background Art
Optical discs such as DVD-RAM and DVD-RW that employ rewritable phase-change optical recording materials are now commonly available. Given the social needs, such as the recent growth of the Internet communities and the increase in the volume of information that must be handled, it is necessary to further increase the number of times information can be written over. In particular, in the management region for the management of directory information and defects, rewrites repeatedly take place at the same location, making the region more prone to deterioration. Deterioration is caused by various reasons. One of them, a contamination phenomenon, will be described below. When a phase-change optical recording material is melted in order to form a mark, diffusion of substances between the recording film and the adjacent protective film material, namely the contamination phenomena, occurs. As the refractive index of the recording film is altered by the contamination phenomena, resulting in a change in the strength of the reproduction signal and a reduction of the quality thereof. In the management region of the optical disc media, renewal of information is in many cases a part of a block, such that rewrites take place with substantially identical information. When the recorded information is identical, the locations of marks and spaces are constant within a margin of error due to uneven rotation, for example. In this case, if the reflectivity of only the mark portions decreases due to the contamination phenomena, the deterioration of data quality would be extremely pronounced.
In order to increase the number of rewrites that can be performed, JP Patent Publication (Kokai) No. 2002-197662 A discloses a technology involving polarity reversal, for example, in DVD-RAM, whereby the marks and spaces are randomly reversed in each rewrite such that the influence of the contamination phenomena can be made as uniform as possible. The RLL (2, 10) modulation (8-16 modulation) used in DVD is a technique for converting user data into edge positions. The modulation technique is thus an edge recording method, so that there is no change in the edge information no matter whether the pattern recorded on the disc is a mark (amorphous) or a space (crystalline). In DVD-RAM, utilizing the property of the 8-16 modulation and the fact that the data region is divided into sectors, a mark or a space is randomly allocated in the head pattern in each sector, thereby preventing only a mark (or a space) from being recorded at a specific location. This is referred to as a polarity reversal method, whereby 100,000 or more rewrites can be performed.
[Patent Document 1] JP Patent Publication (Kokai) No. 2002-197662 A